The disclosure of Japanese Patent Application No. 2000-132636 filed on May 1, 2000, including the specification, drawings and abstract, is incorporated herein by reference in its entirety.
1. Field of Invention
This invention relates to an apparatus and method for controlling negative pressure in internal combustion engines, and more particularly to an apparatus and method for controlling negative pressure in an internal combustion engine provided with a brake booster that utilizes negative pressure generated on a downstream side of a throttle valve disposed in an intake air passage, as a power source for boosting or amplifying pedal pressing force that is applied to a brake pedal.
2. Description of the Related Art
An example of a known apparatus for controlling negative pressure in an internal combustion engine provided with a brake booster for amplifying a brake pressing force is disclosed in, for example, U.S. Pat. No. 6,095,116. The brake booster utilizes a negative pressure generated on a downstream side of a throttle valve disposed in an intake air passage, as a power source for boosting or amplifying a pedal pressing force that is applied by a driver to a brake pedal. If an insufficient negative pressure is supplied from the intake air passage, therefore, the brake booster cannot amplify the pedal pressing force in an appropriate manner.
In view of this situation, the known apparatus as disclosed in U.S. Pat. No. 6,095,116 is adapted to detect a negative pressure applied to the brake booster, and close the throttle valve by a predetermined degree or amount if the negative pressure has not reached a predetermined value. In this case, a large negative pressure is developed in the intake air passage on the downstream side of the throttle valve, and the thus increased negative pressure is applied to the brake booster. Thus, the known apparatus can surely provide a sufficiently large negative pressure to be applied to the brake booster, so that the pedal pressing force (i.e., the force applied to the brake pedal) can be appropriately boosted or amplified.
Upon a cold start of the internal combustion engine, the ignition timing may be retarded from the optimal timing in order to accelerate warm-up of a catalyst, and the like. If the ignition timing is retarded, the temperature of exhaust gas is likely to increase, whereas the output of the engine is reduced. In general, the output of the engine increases with increases in the amount of the air drawn into the engine and in the amount of fuel injected. Thus, in order to accelerate warm-up of the catalyst, and the like, while avoiding a reduction in the output of the engine, it is possible to increase the opening of the throttle valve disposed in the intake air passage while at the same time retarding the ignition timing.
If the opening of the throttle valve increases rapidly upon a cold start of the engine, a large negative pressure is not produced in the intake air passage on the downstream side of the throttle valve, and the negative pressure applied to the brake booster cannot be increased up to a desired or required level. In the above-described known apparatus, if the negative pressure applied to the brake booster fails to reach the desired level, the throttle valve is closed so as to increase the magnitude of the negative pressure. However, if the throttle valve is immediately closed every time the negative pressure applied to the brake booster becomes insufficient, the amount of air drawn into the engine is reduced, and the output of the engine cannot be increased as desired.
It is therefore an object of the invention to provide an apparatus and method for controlling negative pressure in an internal combustion engine, which is able to provide a sufficiently large negative pressure to be applied to a brake booster, without impeding or affecting the operation of the engine.
To accomplish the above and/or other objects, one aspect of the invention provides an apparatus for controlling a negative pressure in an internal combustion engine, comprising a brake booster and a controller. The brake booster amplifies a pedal pressing force that is applied to a brake pedal, by using a negative pressure produced on a downstream side of a throttle valve provided in an intake passage of the engine, as a power source for amplifying the pedal pressing force. The controller determines whether a negative pressure applied to the brake booster has reached a predetermined level when the internal combustion engine is started, and, if the negative pressure has not reached the predetermined level, increases an operating speed of the engine to a predetermined high speed, and then keeps the throttle valve in a small opening state in which an opening amount of the throttle valve is smaller than that established when the internal combustion engine is in a fast idle state, during a period of time in which the engine proceeds to a steady-state operating mode.
In the apparatus as described above, the throttle valve may be kept in a fully closed position during the period of time in which the internal combustion engine proceeds to the steady-state operating mode. It is also possible to keep the opening amount of the throttle valve substantially equal to a throttle opening established during normal idling of the internal combustion engine, during the period of time in which the internal combustion engine proceeds to the steady-state operating mode.
In the apparatus as described above, the brake booster is adapted to amplify the pedal pressing force applied to the brake pedal using, as a power source, a negative pressure (hereinafter called xe2x80x9cintake manifold pressurexe2x80x9d) produced on the downstream side of the throttle valve disposed in the intake air passage. The internal combustion engine can operate or revolve due to inertia without being supplied with the air, until the engine proceeds to the steady-state operating mode after its speed reaches the predetermined high speed. During this self-operating period, the throttle valve can be suitably maintained in the fully closed state without causing any problem to the operation of the engine.
In the apparatus of the invention as described above, if a negative pressure applied to the brake booster (which will be called xe2x80x9cbrake negative pressurexe2x80x9d) is less than a desired level at the time of the start of the engine, the throttle valve is kept in the fully closed state during the period of time in which the engine proceeds to the steady-state operating mode after its speed reaches the predetermined high speed. In this case, a large intake manifold pressure is produced in the intake air passage downstream of the throttle valve, so that the brake negative pressure is accordingly increased. According to the invention, therefore, it is possible to provide the brake booster with a sufficiently large negative pressure without affecting the operation of the internal combustion engine.
Another aspect of the invention involves a method of controlling negative pressure in an internal combustion engine as described above.